Various types of apparatus and methods are known to check or test the shape or contour of gear teeth. Usually, a measuring or sensing head is provided, which is moved in a plane transverse to the axis of a gear retained on the apparatus. The sensing head is kept in engagement with a flank of the gear tooth. The gear may be stationary or rotated and, in order to test involute-type gears, it can be moved along a path tangential to a base circle compatible with the profile of the flank. When the gear is rotated, the measuring sensor is rolled off the gear flank. The contact point of the measuring head of the tangential path, with respect to the base circle of the sensor is used to determine the contour or profile or shape of the gear tooth, with reference, for example, to the center of rotation of the gear tooth. Both right and left flanks--with reference to the center of the gear tooth--can be tested in that way upon engagement of the sensing head with the respective flank.
Methods for so testing the gear teeth, and the associated apparatus to carry out the method, are frequently used to test the flanks of involute gear teeth. The base circle of the gear forms the generatrix for the involute profile. Such apparatus and methods are also suitable to test gear teeth which are curved and somewhat different from involute curves, and which lend themselves to testing by rolling off the gear against the sensing head. The present invention is also suitable for testing such gears. Curves, in space, which are somewhat comparable to involute curves, and can be tested in accordance with prior art processes, as well as with the method and apparatus of the present invention, may be of the Wildhaber-Novikov type. The curve or course of the flank deviates in well known and fixed manner from an involute curve. The only requirement of such other curves which can be tested is that the difference between the actual tooth to the bested and an involute curve is in that region in which the sensing head can be deflected or moved from a base or rest or centered position.
German Pat. No. 32 12 082, Hofler, describes an apparatus and method to test the involute profile of gear teeth. In accordance with this disclosure, a sensor is moved in a direction along an x-axis, for example on a carriage, in the direction of an X-guide path. The origin of the involute curve to be tested is placed in the intersection of the base circle with a line perpendicular to the moving path of the X-coordinate carriage, and passing through the axis of the gear. Two measuring ranges will then result, one each for the right and the left gear teeth, which are located, correspondingly, to the right and to the left of the origin of the involute. The movement path of the carriage of the test apparatus thus must be sufficiently long in order to permit testing of both the right and left gear teeth of gears.
The apparatus, as described in the referenced German Pat. No. 32 12 082, thus becomes complex and bulky since the travel path of the carriage carrying the measuring head must be long in order to permit testing the profiles of right and left gear teeth.
Problems arise when testing gears having internal gearing. The flanks of internal gear teeth extend essentially radially inwardly and a sensing head which operates essentially from an inner towards an outer surface may collide with the gearing during testing. Such collision can be avoided by using sensing heads carried on carrier elements which are angled off or shaped to prevent such collisions. This solution, while permitting testing, is undesirable however since two different sensing heads, one for the right and one for the left flank, must be used and changing sensing heads for testing is time-consuming and leads to inaccuracies.